U.S. patent application number 11/488310 was filed with the patent office on 2008-01-17 for apparatus and method for improved measurement speed in test and measurement instruments.
Invention is credited to Kenneth P. Dobyns, Paul M. Gerlach.
Application Number | 20080012861 11/488310 |
Document ID | / |
Family ID | 38948797 |
Filed Date | 2008-01-17 |
United States Patent
Application |
20080012861 |
Kind Code |
A1 |
Dobyns; Kenneth P. ; et
al. |
January 17, 2008 |
Apparatus and method for improved measurement speed in test and
measurement instruments
Abstract
An apparatus for measuring a parameter of a digitized signal
including a digitizer to digitize an input signal into a digitized
signal, a rasterizer to generate a raster image from the digitized
input signal, a processor to receive the raster image, and a
control interface to receive an input control signal indicating a
request for a measurement. The rasterizer is responsive to the
control signal to generate the raster image from the digitized
input signal, and the processor is responsive to the control signal
to generate a histogram from the raster image.
Inventors: |
Dobyns; Kenneth P.;
(Beaverton, OR) ; Gerlach; Paul M.; (Beaverton,
OR) |
Correspondence
Address: |
THOMAS F. LENIHAN;TEKTRONIX, INC.
14150 S. W. KARL BRAUN DRIVE, P.O. BOX 500 (50-LAW)
BEAVERTON
OR
97077-0001
US
|
Family ID: |
38948797 |
Appl. No.: |
11/488310 |
Filed: |
July 17, 2006 |
Current U.S.
Class: |
345/443 ;
382/168 |
Current CPC
Class: |
G01R 13/0218
20130101 |
Class at
Publication: |
345/443 ;
382/168 |
International
Class: |
G06K 9/00 20060101
G06K009/00; G06T 11/20 20060101 G06T011/20 |
Claims
1. An apparatus for measuring a parameter of a digitized signal,
comprising: a digitizer to digitize an input signal into a
digitized input signal; a rasterizer to generate a raster image
from the digitized input signal; a processor to receive the raster
image; and a control interface to receive an input control signal
indicating a request for a measurement; the rasterizer being
responsive to the control signal to generate the raster image from
the digitized input signal, and the processor being responsive to
the control signal to generate a histogram from the raster
image.
2. The apparatus of claim 1, wherein: the rasterizer is
configurable to generate the raster image having only one column in
response to the control signal.
3. The apparatus of claim 1, wherein: the processor is configurable
to generate each entry of the histogram from a corresponding row of
the raster image.
4. The apparatus of claim 1, further comprising: a user interface
to generate the control signal in response to a user input.
5. The apparatus of claim 1, further comprising: a network
interface to receive the control signal.
6. The apparatus of claim 1, wherein the processor is further
configured to generate a measurement of the digitized signal using
the histogram.
7. The apparatus of claim 1, further comprising: a second
rasterizer configurable to generate a second raster image from the
digitized input signal; and a display configured to display the
second raster image.
8. An apparatus for measuring a parameter of a digitized signal,
comprising: means for digitizing an input signal; means for
receiving a control signal requesting a measurement; means for
rasterizing the input signal into a raster image in response to the
control signal; means for converting rows of the raster image into
entries of a histogram; and means for calculating the parameter
using the histogram.
9. The apparatus of claim 8, further comprising: means for
generating the control signal in response to a user input.
10. The apparatus of claim 8, wherein: the means for digitizing the
input signal further comprises means for digitizing the input
signal into a plurality of digitizing levels; and the means for
rasterizing the input signal into the raster image further
comprises means for rasterizing each digitizing level into a
corresponding row of the raster image.
11. The apparatus of claim 10, wherein the means for rasterizing
each digitizing level into the corresponding row of the raster
image further comprises: means for rasterizing each digitizing
level into a corresponding pixel of the raster image.
12. A method of measuring a parameter of a digitized signal in a
test and measurement instrument, comprising: digitizing an input
signal; receiving a control signal requesting a measurement;
rasterizing the input signal into a raster image in response to the
control signal; converting rows of the raster image into entries of
a histogram; and calculating the parameter using the histogram.
13. The method of claim 12, wherein rasterizing the input signal
into the raster image further comprises rasterizing the input
signal into a single column of the raster image.
14. The method of claim 12, further comprising: selecting a portion
of the input signal spanning a time period; wherein rasterizing the
input signal into the raster image further comprises rasterizing
the portion of the input signal into the raster image.
15. The method of claim 12, wherein: digitizing the input signal
further comprises digitizing the input signal into a plurality of
digitizing levels; and rasterizing the input signal into the raster
image further comprises rasterizing each digitizing level into a
corresponding row of the raster image.
16. The method of claim 15, wherein rasterizing each digitizing
level into the corresponding row of the raster image further
comprises: rasterizing each digitizing level into a corresponding
pixel of the raster image.
17. The method of claim 12, further comprising: initializing the
raster image; and repeating rasterizing the input signal,
converting rows of the raster image into entries of a histogram,
and calculating the parameter using the histogram.
18. The method of claim 12, wherein: rasterizing the input signal
into the raster image further comprises rasterizing the input
signal in a mode selected from a group consisting of an infinite
persistence mode and a variable persistence mode.
19. The method of claim 12, the raster image being referred to as a
first raster image, the method further comprising: rasterizing the
input signal into a second raster image substantially
simultaneously as rasterizing the input signal into the first
raster image; and displaying the second raster image.
20. An article of machine readable code, embodied in a machine
readable medium that, when executed on a machine including a
digitizer, a rasterizer, and a processor, causes the machine to:
digitize an input signal; receive a control signal requesting a
measurement; rasterize the input signal into a raster image in
response to the control signal; convert rows of the raster image
into entries of a histogram; and calculate the parameter using the
histogram.
21. The article of machine readable code of claim 20, further
comprising code that, when executed, causes the machine to
rasterize the input signal into a single column of the raster
image.
22. The article of machine readable code of claim 20, further
comprising code that, when executed, causes the machine to
rasterize each digitizing level of the input signal into a
corresponding row of the raster image.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to test and measurement instruments
and, more particularly, to test and measurement instruments capable
of measuring parameters of digitized waveforms.
[0002] Modem digital oscilloscopes generally provide a measurement
feature whereby specific waveform parameters, such as peak-to-peak
voltage, rise time, pulse width, etc. are calculated for the
acquired waveform data and presented to the user. A central
processing unit (CPU) within the oscilloscope generally computes
these measurements.
[0003] The process begins by moving a digitized waveform from
acquisition memory to CPU memory where it can be processed. The
first step in a measurement calculation is the generation of a
vertical histogram of the digitized levels found within the
waveform. This histogram is used to find key values within the
waveform (high, mid, mean, etc.) These values are, in turn, used to
derive the vertical measurements. Additionally, these values are
used to allow the extraction of the crossing information necessary
for the calculation of timing measurements.
[0004] Unfortunately, this approach to the generation of
measurements requires moving the entire waveform record to the CPU
memory space. Furthermore, the CPU is typically designed for
general-purpose computing, not for the specific purpose of
manipulating waveform data to generate a histogram. As a result,
the overall waveform throughput rate, a key feature of a modern
digital oscilloscope, is reduced. In order to keep the waveform
throughput high, most oscilloscopes update their measurements
infrequently. Consequently, the digital oscilloscope is unable to
efficiently perform further functions using the measurements, such
as a statistical analysis of the measurements.
[0005] Accordingly, there remains a need for a test and measurement
instrument having an improved measurement speed.
SUMMARY
[0006] An aspect of the invention includes an apparatus for
measuring a parameter of a digitized signal including a digitizer
to digitize an input signal into a digitized input signal, a
rasterizer to generate a raster image from the digitized input
signal, a processor to receive the raster image, and a control
interface to receive an input control signal indicating a request
for a measurement. The rasterizer is responsive to the control
signal to generate the raster image from the digitized input
signal, and the processor is responsive to the control signal to
generate a histogram from the raster image.
[0007] Another aspect of the invention includes a method of
measuring a parameter of a digitized signal in a test and
measurement instrument. The method includes digitizing an input
signal, receiving a control signal requesting a measurement,
rasterizing the input signal into a raster image in response to the
control signal, converting rows of the raster image into entries of
a histogram, and calculating the parameter using the histogram.
[0008] The foregoing and other aspects of the invention, and
advantages thereof, will become more readily apparent from the
following detailed description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a block diagram of an apparatus for measuring a
parameter of a digitized signal according to an embodiment of the
invention.
[0010] FIG. 2 is a block diagram of a raster image.
[0011] FIG. 3 is a diagram illustrating the relationship in the
apparatus of FIG. 1 of digitizing levels of a digitized signal and
pixels of a raster image as shown in FIG. 2.
[0012] FIG. 4 is a block diagram of an apparatus for measuring a
parameter of a digitized signal according to another embodiment of
the invention.
[0013] FIG. 5 is a flowchart of a method of measuring a parameter
of a digitized signal according to an embodiment of the
invention.
[0014] FIG. 6 is a flowchart of a method of measuring a parameter
of a digitized signal according to another embodiment of the
invention.
[0015] FIG. 7 is a flowchart of a method of measuring a parameter
of a digitized signal according to another embodiment of the
invention.
DETAILED DESCRIPTION
[0016] As described above, measurements made on digitized waveforms
are made infrequently so that the waveform throughput rate is not
adversely affected. To achieve an increased measurement speed, a
rasterizer can be used to calculate the vertical histogram.
[0017] As used in this discussion, a rasterizer is any device or
apparatus that processes digitized waveform data and generates a
raster image formed of pixels. Thus, the rasterizer converts data
into a format suitable for digital displays using pixels to present
images.
[0018] Modem digital oscilloscopes generally contain a high-speed
rasterizer for drawing acquired waveforms. In order to achieve high
waveform throughput, data movement must be kept to a minimum. Thus,
these rasterizers are located near the acquisition hardware where
they have access to waveform data as it is acquired.
[0019] In order to draw waveforms that emulate a traditional analog
CRT, rasterizers usually contain hardware that implements a
grayscale attack and decay function on a digital or pixelated
display. A side effect of this feature is that these rasterizers
maintain a multi-bit intensity for each display pixel that they
create. Thus, a value corresponding to the intensity is stored for
each pixel.
[0020] There are a variety of ways to adjust the intensity of a
pixel. In one in particular, a "dots only" mode, individually
acquired points are added to the raster image. While most
rasterizers attempt to draw vectors (connecting lines) between
individual acquisition points, this feature can be disabled to draw
one pixel per acquisition point without filling in any intervening
points.
[0021] By placing a rasterizer in a "dots only" mode, it can be
used to generate a histogram by "rasterizing" the waveform into a
single column, for example. As the waveform is rasterized, each
data point increments, by one, the intensity of the pixel that
corresponds to that digitizing level. The bit-depth of the
rasterizer controls how many waveform points can be accumulated
into the histogram without risk of data saturation. At the
completion of the rasterization process, the single-column raster
image contains a complete histogram of the input data.
[0022] Although rasterization generally includes the conversion of
some form of data into a two-dimensional pixelated representation
of that data, rasterization, as used in this discussion
specifically includes the degenerate case of conversion of the data
into a one-dimensional row or column of pixels.
[0023] Furthermore throughout this discussion, horizontal rows and
vertical columns are used to describe the relationships of pixels,
particularly within a raster image. However, one skilled in the art
will understand that particular designations of rows and columns
are used for convenience of description and may be used
interchangeably.
[0024] A rasterizer is generally faster than the CPU at
manipulating the waveform data. The rasterizer may be specifically
designed for this purpose. In addition, the waveform data itself
does not need to be moved to the CPU to calculate measurements. In
one example, only the histogram itself, which is significantly
reduced in size, need be moved to and processed by the CPU. Thus,
the rasterizer can generate the histogram data, improving the speed
with which measurements can be made.
[0025] FIG. 1 is a block diagram of an apparatus for measuring a
parameter of a digitized signal according to an embodiment of the
invention. The apparatus 10 includes a digitizer 12, a memory 14, a
rasterizer 16, a processor 18, and a control interface 20. The
digitizer 12 digitizes an input signal into a digitized signal. The
digitized signal is stored in the memory 14.
[0026] The digitizer 12 may be any variety of digitizer using any
style of signal acquisition capable of transforming a signal into a
digital representation of that signal. For example, the digitizer
12 may include a successive approximation analog-to-digital
converter (ADC) operating in a real-time sampling mode, sampling as
often as possible. Alternatively, the digitizer 12 may include a
direct conversion ADC operating in an equivalent-time sampling
mode, sampling at a determined time period after a trigger. Any
combination of digitizer and operating mode may be used such that a
digitized representation of the signal is stored in the memory
14.
[0027] The processor 18 may communicate directly or indirectly with
the rasterizer 16. For example, a data bus 17 may link the
processor 18 and the rasterizer 16. In addition, the processor 18
may communicate with the rasterizer 16 through a common memory. The
common memory may be the memory 14 or another memory separate from
the memory 14.
[0028] Furthermore, although the memory 14 has been illustrated in
FIG. 1 as located between the digitizer 12 and the rasterizer 16,
such a memory is not required. For example, the digitizer 12 may
send digitized data to the rasterizer 16 rather than through the
memory.
[0029] As used herein, a processor 18 may include microprocessors,
microcontrollers, digital signal processors (DSP), field
programmable gate arrays (FPGA), programmable logic devices (PLD),
or the like. Any such device that can manipulate digital data may
be used as a processor 18.
[0030] During general operation, the digitized signal is rasterized
in the rasterizer 16 into a raster image to be displayed as a two
dimensional (m.times.n) array of pixels on the display 22. However,
if an input control signal requesting a measurement is received by
the control interface 20, the rasterizer 16 generates a raster
image in response to this control signal. The raster image may be a
1.times.n raster image with only one column. The processor 18 then
generates a histogram from this raster image.
[0031] FIG. 2 is a block diagram of a raster image. A raster image
40 is formed of multiple pixels 42. The pixels 42 may be arranged
in an m.times.n array of rows 46 and columns 44. For example, 44-2
represents the second column 44. A raster image 40 may have any
number of rows 46 and columns 44.
[0032] FIG. 3 is a diagram illustrating the relationship in the
apparatus of FIG. 1 of digitizing levels of a digitized signal and
pixels of a raster image as shown in FIG. 2. FIG. 3 includes a
graph of an input signal 62 having a voltage varying over time.
Digitizing levels 60 describe voltage ranges over which the input
signal 62 are digitized into the same digitizing level 60. For
example, two digitizing levels 60-1 and 60-2 are illustrated
corresponding to two voltage ranges.
[0033] In general operation, the rasterizer 16 may create a raster
image 40 to be displayed on a display 22. Each pixel 42 may be
associated with a memory location or register storing a multi-bit
representation of that pixel 42. The columns 44 may represent
different times associated with the waveform. The rows 46 may
represent different amplitudes. For example, a first sample of the
waveform at a first time may be rasterized into a pixel 42 at a
first column 44-1 and a first row 46-2. A second sample of the
waveform at a second time having the same amplitude as the first
sample may be rasterized into a different second column 44-2 and
the same row 46-2. The rasterizer 16 modifies the values
corresponding to the pixels 42 to create a raster image
representing the input signal 62. Multiple columns 44 may be used
to represent the time span displayed on the display 22.
[0034] In response to the control signal, the rasterizer 16 may
rasterize the input signal 62 into a single-column raster image 64.
Every sample of the digitized input signal at a particular
digitizing level 60 is rasterized into a corresponding pixel 42 of
the single-column raster image 64. For example, samples within
digitizing level 60-2 are rasterized into pixel 42-2. In contrast
to the general operation of the rasterizer 16 described above, even
though the input signal 62 may be varying over time, all samples
are rasterized into a single column 44 of the single-column raster
image 64.
[0035] The apparatus 10 may include storage 24 or other memory
including instructions or code enabling the rasterizer to rasterize
in response to the control signal. The code in the storage may
cause the rasterizer 16 to change its function to rasterize the
input signal into a single-column raster image 64.
[0036] During the rasterization into the single-column raster image
64, the rasterizer 16 may increment a pixel in the single-column
raster image 64 corresponding to each sample of the digitized input
signal. In one example, the value stored in a pixel 42-1 is
incremented by one when rasterizing a sample with a corresponding
digitizing level 60-1. Similarly, the value stored in a pixel 42-2
is incremented by one when rasterizing a sample with a
corresponding digitizing level 60-2. Thus, all samples of one
particular digitizing level 60 increment the value stored at the
pixel 42 associated with that digitizing level 60.
[0037] Although incrementing the value in a pixel 42 by one has
been described, any technique for incrementing may be used. For
example, initial samples associated with a pixel 42 may increment
the value by one. However, as the value stored in the pixel 42
increases, a greater number of samples may be required in order to
increment the value by one. For example, if a value stored in a
pixel 42 is one half of its maximum value, two samples may be
needed in order to increase the value by one. Thus, the value of a
pixel 42 need not have a one-to-one relationship with the number of
samples rasterized into that pixel. Any encoding may be used as
desired.
[0038] As a result of rasterizing the input signal 62 into a
single-column raster image 64, the time information associated with
the samples of the input signal 62 may be discarded. Thus, the
remaining data is the distribution of the input signal 62 over the
digitizing levels 60. In other words, the data within the
single-column raster image 64 is a histogram of the input signal
62.
[0039] Although a single-column raster image 64 has been described,
a multi-column raster image 66 may be used. In particular, if the
depth of one pixel 42 of a single-column raster image 64 is not
sufficient to hold a desired count of samples for the histogram,
multiple pixels may be used to extend the maximum number of
samples. For example, if one pixel 42 has a bit depth of 8, and can
store a count of up to 255, an additional pixel 42 having a bit
depth of 8 may be used, giving the combination an ability to store
a count of up to 65535. Although one particular coding scheme for
representing a count of samples in multiple pixels has been
described, other coding schemes may be used. For example, a value
in a first pixel is incremented until the count reaches a maximum
count for the first pixel. Then a value in a subsequent pixel is
incremented. Each time a value in a pixel reaches a maximum count,
further samples are added to subsequent pixels. Thus, with two
pixels having bit depths of 8 bits, counts for 255 samples may be
stored in each pixel, giving the sum of two pixels an ability to
store a count of up to 510.
[0040] In the example illustrated in FIG. 3, the samples
corresponding to one digitizing level 60 are all rasterized to be
contained within the pixels 42 of one row 46 of the multi-column
raster image 66. For example, samples within the digitizing level
60-1 are rasterized into the pixels 42-1-1 and 42-2-1 of row 46-1.
In contrast to a raster image to be displayed on a display 22, the
multi-column raster image 66 may not have any time information. The
raster image for display purposes may use the columns 44 to
indicate a different time. However, in the multi-column raster
image 66, the additional pixel 42-2-1 of the row 46-1 is used for
extended storage of the sample count.
[0041] Although two pixels 42 have been illustrated in the
multi-column raster image 66, any number of pixels 42 of a row may
be used. Furthermore, although additional pixels 42 specifically
referencing a multi-column raster image 66 have been illustrated in
adjacent columns 44-1 and 44-2, the additional pixels 42 may be
located anywhere in the raster image. For example, two pixels 42
within one column 44 may correspond to one digitizing level 60, and
two columns 44 are used to provide enough pixels 42 of all of the
digitizing levels 60.
[0042] Regardless of the number of columns 44 used, the raster
image is then sent by the rasterizer 16 to the processor 18. If the
raster image is a multi-column raster image 66, the processor 18
can collapse the rows 46 into entries of the histogram. Although,
the processor 18 is described as generating the histogram, the
generation may only involve copying the data from the raster image.
In particular, if the raster image is a single-column raster image
64, no additional processing is needed to generate the histogram
beyond converting the data of the single-column raster image 64
into a format suitable for the processor 18 to calculate
measurements.
[0043] As a result of the rasterizing into a single or multi-column
raster image 64 or 66, the data used to calculate a histogram that
is sent to the processor 18 is no longer the entire waveform data.
In one example, the raster image alone, occupying less storage
space than the source waveform, is sent to the processor 18. Thus,
the time needed to transfer the larger waveform data is no longer
needed. Furthermore, the rasterizer 16, specifically designed for
translating digitized data into a raster image, may translate
digitized data faster than the accompanying processor 18. As a
result, the time required by the processor 18 to generate a
histogram is significantly reduced.
[0044] Although an example including transferring the raster image
alone has been described above, some or all of the source waveform
data may be transferred to the processor 18 for some measurements.
For example, time-based measurements, such as periods and pulse
widths, may need the waveform data in order to generate
threshold-crossing information for such measurements. However, even
though the entire source waveform data may be transferred to the
processor 18, the time required to generate such measurements is
still reduced as a result of the processing efficiency of the
rasterizer 16 described above.
[0045] Once the histogram is generated by the processor 18, the
processor 18 may generate any number of measurements from the
histogram, including providing the histogram itself as the desired
measurement. As a result of most if not all of the calculation for
a histogram being offloaded to the rasterizer 16, the processor 18
has more time for other tasks. Specifically, since data for
generating the histograms may come at a faster rate and the
processor has available time, more histograms may be generated and
more corresponding measurements may be calculated. Thus, the
overall rate at which measurements can be updated is increased.
[0046] Although the processor 18 has been described as generating a
histogram using a single raster image, similar to the way that
multiple pixels of one row may be used to extend the maximum count,
multiple raster images may be combined together into one histogram.
For example, the rasterizer 16 may rasterize a first half of the
digitized waveform into a first raster image, and rasterize a
second half of the digitized waveform into a second raster image.
Both raster images may be transferred to the processor 18 for
calculating the histogram.
[0047] Referring again to FIG. 1, in order to allow a user to
request a measurement, the apparatus 10 may include a user
interface 26. The user interface 26 generates the control signal in
response to a user input. The user interface 26 may include any
type of interface, including touch screens, buttons, dials,
sliders, keyboards, or the like.
[0048] In addition, the apparatus 10 may include a network
interface 28 to receive the control signal. Control signals may be
generated at remote locations. These control signals may be
communicated to the apparatus 10 through the network interface 28.
Thus, measurements may be made in response to control signals
generated external to the apparatus 10.
[0049] In another embodiment, an apparatus for measuring a
parameter of a digitized signal includes means for digitizing an
input signal, means for receiving a control signal requesting a
measurement, means for rasterizing the input signal into a raster
image in response to the control signal, means for converting rows
of the raster image into entries of a histogram, and means for
calculating the parameter using the histogram.
[0050] The means for digitizing an input signal may include the
digitizer 16 described above and any associated control and storage
to convert the input signal into digitized data. The means for
digitizing the input signal may further include means for
digitizing the input signal into multiple digitizing levels.
[0051] The means for receiving a control signal requesting a
measurement may include circuitry such as the control interface 20
described above. For example, the means for receiving a control
signal may be capable of monitoring a user interface 26 for a
control signal. In addition, the means for receiving the control
signal may include a processor monitoring the user interface 26
described above for a control signal, the network interface 28
described above, or combinations of such interfaces.
[0052] The means for rasterizing the input signal into a raster
image in response to the control signal may include a rasterizer 16
described above. Any such rasterizer capable of rasterizing an
input signal into a raster image, such that one or more pixels of
the raster image can represent a count of samples at a particular
digitizing level, may be used. Thus, the means for rasterizing the
input signal may include means for rasterizing each digitizing
level into a corresponding row of the raster image. In particular,
each digitizing level may be rasterized into a corresponding
pixel.
[0053] The means for converting rows of the raster image into
entries of a histogram and the means for calculating the parameter
using the histogram may include one or more processors 18 as
described above. For example, a FPGA may manipulate the data of a
raster image, collapsing a multi-column raster image 66 into a
histogram, and a microcontroller may receive the histogram and
calculate measurements from the histogram. Any combination of
processors, or a single processor may be used.
[0054] FIG. 4 is a block diagram of an apparatus for measuring a
parameter of a digitized signal according to another embodiment of
the invention. In FIG. 4, a second rasterizer 30 is coupled to the
digitizer 12. The second rasterizer 30 may generate a second raster
image of the digitized input signal. The second raster image may be
a raster image suitable for displaying the waveform on a display
22.
[0055] Although the rasterizing of the input signal 62 into a
single-column raster image 64 or a multi-column raster image 66 has
been described above in contrast to the general operation of the
rasterizer 16, such operations are not mutually exclusive and may
be performed at substantially the same time. For example, the input
signal 62 may be rasterized into a single-column raster image 64 by
rasterizer 16 in parallel with rasterizing the input signal 62 into
another m.times.n raster image for presenting on a display in the
second rasterizer 30. As a result, data of the input signal 62 that
is used to generate a histogram is not lost, and may be displayed
with the histogram and any derived measurements.
[0056] Furthermore, any memory or storage used to store a raster
image may be independent of a memory or storage used to store a
raster image for general display purposes. For example, each raster
image may be stored in a different portion of the memory 14
described above. Thus, the creation of each raster image may be
performed independently.
[0057] In addition, even though the raster images have been
described as being generated from the same data, the raster images
may be generated from different sets of data. For example, a first
amount of data suitable for generating a first m.times.n raster
image for display purposes may be smaller than a second amount of
data used to generate a second single or multi-column raster image
for generating a histogram with a desired accuracy. Thus, a new
raster image for display may be generated each time the first
amount of data is received, while the second amount of data is
being accumulated for the second raster image.
[0058] FIG. 5 is a flowchart of a method of measuring a parameter
of a digitized signal according to an embodiment of the invention.
The method includes digitizing an input signal in 80, receiving a
control signal requesting a measurement in 82, rasterizing the
input signal into a raster image in response to the control signal
in 84, converting rows of the raster image into entries of a
histogram in 86, and calculating the parameter using the histogram
88. Thus, receiving a control signal requesting a measurement
results in a parameter of a digitized signal being calculated using
a raster image of the input signal.
[0059] Digitizing an input signal in 80 includes converting the
input signal into a digital representation. Thus, the digitized
input signal is converted into multiple digitizing levels. When
rasterized into a raster image in 84, each row of the raster image
may correspond to one digitizing level. Thus, there may be as many
rows in the raster image as there are digitizing levels. In
addition, as described above, each row may include only one pixel
so that each digitizing level corresponds to one pixel.
[0060] Alternatively, the digitizing in 80 and rasterizing in 84
may be performed such that the number of digitizing levels is not
equal to the number of rows of the raster image. As a result, one
digitizing level may span more than one pixel, and may increase the
values of those pixels appropriately. In such a case, each pixel or
row of the raster image may be changed by an amount less than the
amount that would be used if there was a one-to-one relationship of
pixels to digitizing levels.
[0061] Furthermore, even though the number of pixels in a column
and the number of digitizing levels may not be equal, a one-to-one
relationship may still be maintained. For example, if the number of
digitizing levels is less than the maximum number of pixels in a
column of a raster image, a subset of the pixels of may be used to
create a one-to-one relationship. Thus, each digitizing level may
be mapped to an associated pixel even though the number of
digitizing levels is different from the number of pixels in a
column.
[0062] FIG. 6 is a flowchart of a method of measuring a parameter
of a digitized signal according to another embodiment of the
invention. In particular, rasterizing the input signal into the
raster image in 84 may include rasterizing the input signal into a
single column 90 of the raster image. Thus, as described above,
each row or pixel represents an entry of the histogram. The
converting of rows of the raster image into entries of a histogram
in 86 may include copying the data of the raster image into the
histogram.
[0063] In addition, converting rows of the raster image in 86 may
include accessing the data structure of the raster image as a
histogram. Since there may be a one-to-one correspondence with a
value stored in a pixel of the raster image and a corresponding
entry of a histogram, no additional processing may be needed. Thus,
the data may be used by a processor by accessing the data of the
raster image as if the data was a histogram. Alternatively, the
data may be moved, copied, or otherwise manipulated to be in a
format acceptable to calculating the parameter using the histogram
in 88.
[0064] Furthermore, the method may include selecting a portion of
the input signal spanning a selected time period. A user may desire
to calculate measurements using a histogram formed over a
particular time period of the input signal. Thus, a portion of the
input signal spanning the time period may be selected. The portion
is then rasterized into the raster image in 84.
[0065] Rasterizers may rasterize an input signal in a variety of
modes. As described above, values of pixels may simulate the
intensity of analog CRT displays. In order to simulate the lifetime
of a dot on an analog CRT display, a rasterizer may use a decay
function to reduce the intensity of pixels. However, in one
example, when calculating a histogram, the values do not decay.
Thus, the method may include rasterizing the input signal in an
infinite persistence mode. As a result, the values in pixels are
not reduced over time to simulate analog CRT displays.
[0066] Alternatively, the rasterizer may use a decay function in a
variable persistence mode while rasterizing the input signal in 84.
Thus, over time, the value of pixels of the raster image will
decrease. As described above, there may be a maximum count for each
pixel or row of a raster image. By reducing the counts stored in
the pixels over time, a measurement of more samples than the
maximum count may be made. Without reducing the counts, if new
samples are added to a pixel or row that is already at the maximum
count, the information provided by that sample is lost. While the
count within a pixel or row may no longer represent an exact count
of all samples at the associated digitizing level, the count may
still be an indicator of the number of samples at the associated
digitizing level beyond the maximum count without losing all of the
information of the latter samples.
[0067] In addition, since the rasterizer may rasterize the input
signal with infinite persistence, it may be necessary to reset the
values in the pixels. For example, if a new signal is applied, a
new measurement is selected, or a sufficient time has passed, the
values of the pixels may be reset so that subsequent measurements
can be made with current data. Thus, the method may include
initializing the raster image, and repeating rasterizing the input
signal 84, converting rows of the raster image into entries of a
histogram 86, and calculating the parameter using the histogram 88.
As a result, a new histogram may be generated allowing for new
measurements to be calculated.
[0068] FIG. 7 is a flowchart of a method of measuring a parameter
of a digitized signal according to another embodiment of the
invention. The input signal is rasterized into a second raster
image in 92. The second raster image is displayed in 94. The
rasterization into the second raster image in 92 may occur
substantially simultaneously as the input signal is rasterized in
84. Thus, the second raster image may be displayed in 94
substantially simultaneously as displaying a measurement calculated
in 88.
[0069] Furthermore, an above-mentioned method may be implemented
through an article of machine readable code, embodied in a machine
readable medium that, when executed, causes the machine to perform
the method. For example, a rasterizer may be controlled through
firmware or other code executable by the rasterizer. Such code may
be stored in a storage device such as storage 24 illustrated in
FIG. 1. Thus, when a control signal is received, the code causes
the rasterizer to rasterize the input signal into a raster
image.
[0070] Furthermore, the machine readable code may include code for
a variety of processors that may execute code. Thus, the machine
readable code may include, for example, code such as processor
specific and rasterizer specific code.
[0071] As a result, a device may be manufactured that has the
capability of generating a histogram by rasterizing an input
signal, but the capability is not implemented. However, through a
subsequent update, whether software, firmware, or other code, the
functionality of generating a histogram by rasterizing an input
signal may be enabled in the device.
[0072] Although particular embodiments have been described, it will
be appreciated that the principles of the invention are not limited
to those embodiments. Variations and modifications may be made
without departing from the scope of the invention as set forth in
the following claims.
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